Impact of age on neutrophil phagocytic reaction with different capsular serotypes of Klebsiella pneumoniae.

Background: Although the prevalence of K pneumoniae liver abscess is higher in patients older than 55 years, the possible relationship of age with decreased phagocytic function of the patients with Klebsiella pneumoniae liver abscess has not been investigated. Our aim was to determine whether susceptibility to K pneumoniae infection depended on age-related impairment of phagocytic function.

Methods: The study enrolled 42 subjects in three age groups: younger than 40 years (n=10), 40-65 years (n=12), and older than 65 years (n=20). Seventy-five strains of K pneumoniae were investigated, including liver abscess isolates (n=25) and blood isolates from the patients without liver abscesses (n=50). The rate of phagocytosis of K1/K2 (n=36) and non-K1/K2 (n=39) K pneumoniae by neutrophils was determined using flow cytometry and compared among the three age groups.

Results: The rate of phagocytosis of serotype K1/K2 isolates was significantly lower in the middle-aged group than that in the younger group (p=0.015) and significantly lower in the older group than those in the middle-aged and younger groups (p=0.025 and p<0.01). In contrast, the rate of phagocytosis of non-K1/K2 isolates was similar in all three age groups at 60 minutes (66.4±1.85%, 65.2±2.0%, and 62.3±1.81%; p=not significant).

Conclusions: Thus, as age increases, the ability of neutrophils to phagocytose virulent K1/K2 K pneumoniae decreases. This finding may account for the higher prevalence of K pneumoniae liver abscesses in older patients.